1. Field of the Invention
The present invention relates generally to archery bows and more particularly pertains to an improved compression molded archery bow limb for use in a compound bow and method for manufacturing the same.
2. Description of the Prior Art
Archery bow limbs perform the important function of storing energy when the archer draws the bowstring. When the bowstring is drawn, the pre-stressed bow limbs, which are typically made of resilient material, are further flexed to store additional energy. When the bowstring is released, the stored energy propels the arrow.
In conventional compound bows, the limb is typically formed of a single element of rectangular cross section, wherein one end is attached to the bow handle and the other end has a limb tip slot formed therein, in which an eccentric wheel is mounted.
Reinforced glass fiber materials have been utilized in archery bow limbs for a number of years. In some instances, the limb profile is machined from extruded solid glass fiber billets, and in other instances the limb profile is machined from pre-formed compression molded billets, which in some cases may be pre-formed to such near net shape that only secondary machining operations are required to remove excess material from the limb tip area and from the butt slot area, where the limb is joined to the handle. In all such cases, the secondary machining operations are costly and time consuming. Further, the machining operations result in the severing of load bearing fibers which reduces the maximum limb operating stress level and the fatigue life of the limbs.
To lessen the problems associated with machining the reinforcing glass fiber material, several processes have been developed, such as those disclosed in U.S. Pat. Nos. 4,649,889; 4,660,537; and 4,735,667. More recently, there is disclosed in U.S. Pat. No. 5,141,689, issued to G. Simonds, a method of forming a partial limb tip slot in a molded limb profile, and then severing the remaining glass fibers in the limb tip slot area to form the limb tip. This method reduces the number of glass fibers that are severed so that the fatigue life of the resultant limb tip is substantially improved, and the necessity of providing reinforcement washers to the limb tip slot is avoided. It is not believed, however, that a glass fiber limb for a compound bow has been produced which completely avoided having to sever glass fiber filaments when the limb tip slot was formed.
Further, it was popularly believed (see, for example, U.S. Pat. No. 4,735,667, issued to R. Johnson) that glass fiber limbs should be of a substantially constant cross sectional area in order to maintain a constant glass fiber to resin ratio in the limb.
Thus far the discussion has been concerned with conventional compound bows formed with single element glass fiber limbs of rectangular cross section. A different approach is disclosed in U.S. Pat. No. 4,350,138, issued to J. Caldwell. The limb portions-disclosed therein are formed of left and right limb portions. Significantly, the limb portions disclosed therein are not compression molded, and it is not believed that any such split limb portions have been formed by compression molding despite the fact that the compression molding of limbs has been widely known for many years. More contemporaneous versions of such split limbs are, for example, being sold by Hoyt U.S.A. under the Alpha Tec mark and by High country under the Split Force mark.
The present invention is concerned with a method for manufacturing discrete compression molded archery bow limb portions and the archery bow limbs produced thereby. The limb portions comprise compression molded upper left and right limb portions and compression molded lower left and right limb portions. In this manner, the respective left and right limb portions form the limb tip slots and the costly and time-consuming limb tip slot machining process is avoided, together with the attendant disadvantages associated with such machining, namely, the reduction in the maximum limb operating stress level and the reduction in the limb fatigue life. Further, and contrary to the teaching of the prior art, the upper and lower left and right limb portions may be provided with a varying cross sectional lengthwise profile so that the glass fiber to resin ratio may be made higher in the limb portion area which experiences high stress and lower in the limb portion area in which perhaps more stiffness is desired. Still further, it is desirable that the complementary left and right limb portions have identical glass fiber to resin ratios throughout the length of the limbs and identical mirror image physical configurations and that is achieved through the present invention.
The method of the present invention comprises inserting a moldable slug having a plurality of longitudinally oriented resin impregnated predominantly glass fiber filaments into a limb portion profiling mold. The limb portions comprise a right limb portion and a left limb portion. The mold consists of two halves, the first half containing a female cavity profiled to provide the configuration of the right limb portion in axial alignment with the configuration of the left limb portion, and a second half having a mating male section. The first cavity is profiled to provide the configuration of the right limb portion and the second cavity is profiled to provide the configuration of the left limb portion. The cavities are in parallel relationship with each other and are connected along their longitudinal axis. Each cavity receives a predetermined volume and weight of continuous longitudinal fibrous reinforcement material and plastic resin matrix material. Heat and pressure are applied during initial curing and the uncured end is removed. The slug is then finally cured, either in its entire length or after being severed into a left limb portion and a right limb portion.
Accordingly, it is an object of this invention to provide a method of manufacturing compression molded discrete left and right archery bow limb portions, and the archery bow having limb portions produced thereby.
It is a further object of this invention to provide a method of manufacturing compression molded archery bow limb portions having varying cross sectional lengthwise profiles, and the archery bow having limb portions produced thereby.
Other objects and attendant advantages of this invention will be readily appreciated as the same become more clearly understood by references to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof.